<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>p4_居中测试</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    .card{
      width: 200px;
      height: 300px;
      background-color: pink;
      border: 5px solid #000;
        /* 卡片在页面中居中 */
        margin: 0 auto;
        /* 文字水平居中 */
        text-align:  center;
        /* 文字垂直居中 */
        line-height: 300px;
    }
    .main{
      background-color: darkgrey;
    }
    .center{
      width: 1000px;
      background-color: white;
      margin: 0 auto;
    }
  </style>
</head>
<body>
<div class="main">
  <div class="center">
    <div class="card">我是内容</div>
    <div class="card">我是内容</div>
    <div class="card">我是内容</div>
    <div class="card">我是内容</div>
  </div>
</div>

</body>
</html>